The present invention relates generally to a combined alternator compressor unit for providing both the electrical energy generating function and air conditioner refrigerant pumping function in an automotive vehicle.
Automotive vehicles have customarily included an internal combustion engine as a prime mover which, in addition to propelling the vehicle, drives a number of ancillary devices. The engine ordinarily drives an electrical generator or alternator and several pumps including an air conditioner pump or compressor.
Typically the alternator and refrigerant compressor will each be driven from the engine crankshaft by way of V-belts and pulleys. The alternator typically revolves at high speed to generate a relatively high frequency alternating voltage. With such relatively high frequency alternating voltages stator core losses are normally relatively high, thereby decreasing the efficiency of the alternator.
Typically compressors are actuated by means of an electromagnetic clutch. Much of the time the electromagnetic clutch is not actuated and the compressor pulley is freewheeling and contributes nothing to the loading of the engine except frictional losses. When the system calls for the compressor to pump refrigerant, the clutch is actuated and causes the compressor pulley to drive the compressor.
In some prior art systems the alternator and compressor have been combined into one unit. One example of such a combined alternator compressor unit is disclosed in U.S. Pat. No. 4,095,922 which is assigned to the same assignee of the present application. In this structure the magnetic field for the altenator is generated by a rotating ring of multiple permanent magnets whose rotating magnetic flux field is cut by three sets of stationary coils associated with a stator to thereby generate electric voltages in the coils. The coils are arranged in a toroidal configuration in the stator core slots and the stator is concentrically disposed within the permanent magnet ring. The coils are electrically connected in a Delta configuration. The generated voltage is a function of the velocity of the engine and the rotational speed of the alternator. The required voltage is a function of the system demand for electrical energy. The generated voltage must therefore be controlled to match the required voltage for the most efficient operation of the system.
Some prior art alternators have been provided wherein the excitation field is provided by a rotating electromagnetic coil. Such alternators require sliding contact members in the form of slip rings and brushes to connect the rotating coil to a source of direct voltage. A disadvantage of these alternators is that such sliding contact members are subject to wear and therefore require periodic servicing.
One of the difficulties with prior art alternators has been that the generated electric voltage could be controlled only at considerable expense. Thus, in known alternators of this type one technique which has been used for regulating the voltage is to insert silicon controlled rectifiers (SCR's) in the power circuit. This is undesirable, as it requires control of a large amount of power. Controlling the full alternator power output via this SCR voltage regulator is expensive.
Other prior art alternators have been provided with stationary exciter coils as the only source of alternator magnetic field flux. One patent disclosing such a structure is U.S. Pat. No. 3,493,800. A disadvantage of this type of structure is that a considerable amount of excitation field current must be provided to generate the necessary magnetic field strength. This complicates control of the generated voltage since a relatively large amount of excitation current must be controlled. Also, the excitation winding needs to be fairly bulky which is undesirable in automotive applications where space and weight must be kept to a minimum.
In some permanent magnet excited alternators one technique which has been used for controlling the generated voltage has been to render the available magnetic flux variable by premagnetization. To this end, the stationary armature of the machine is provided with a direct current carrying ring winding through which a variable tangential premagnetization is imparted to the core of the armature in order to control the available magnetic flux. In this type of control arrangement it has been found to be particularly advantageous to at least partially combine the direct current carrying ring winding, which effects premagnetization, with the induced current operating winding. With such an arrangement a comparatively simple device is provided in which the regulation of the available magnetic flux enables control of the generated voltage.
A permanent magnet excited electric generator wherein the excitation magnetic flux is controlled by a direct voltage control winding is disclosed in U.S. Pat. No. 3,411,027. The electric generator includes a controlled magnetomotive excitation force which is generated by permanent magnets and a control coil. The useful magnetic flux, and therefore the generated voltage, is controllable by varying the direct voltage applied to the control coil. The magnetomotive force generated by the coil is combined in shunt relationship with the magnetomotive force generated by the permanent magnets and therefore increases or decreases the resultant useful excitation flux, depending upon the polarity and magnitude of the shunt excitation voltage. A disadvantage of this arrangement is that the coil and permanent magnets are spaced axially thus resulting in a rather large axial dimension for the alternator. The large axial dimension requires additional space and the use of a plurality of bearings for the alternator unit.
It is therefore desired to provide a combined alternator-compressor unit having a small axial dimension wherein the alternator magnetomotive excitation force is generated by permanent magnets and a field coil and wherein the alternator is mounted on a single bearing.
It is also desired to provide a combined alternator-compressor including permanent magnets and a stationary control coil to provide brushless, easily controlled magnetomotive excitation for the alternator.
It is furthermore desired to provide a brushless compact alternator-compressor unit wherein the permanent magnets and excitation coil are concentrically arranged in a compact, lightweight structure which is easy to assemble and has small electromagnetic losses.